**3.8 Shell growth**

*Current Topics in Biochemical Engineering*

**3.5 Synthesis of gold nanoparticles**

bottle for later use.

**3.6 Seeding process**

**3.7 Gold hydroxide solution**

of the silica template solution was magnetically stirred for 5 min with 50 μl of APTES in an 80 ml glass flask. The solution was left still overnight at room temperature. The opaque white functionalized silica particles precipitated in the solution leaving a clear fluid at the top. To separate the functionalized silica, the mixture was centrifuged at 6000 rpm for 1.5 min and washed in deionized water three times.

The method presented by Abdollahi et al. [10] was followed to elaborate the GNPs. First, 100 ml of deionized water at room temperature was placed in a 140 ml flask under magnetic agitation. Then 1 ml of 1% HAuCl4 solution, 2 ml of 1% trisodium citrate, and 1 ml of freshly made 0.075% NaBH4 in 1% trisodium citrate were added in that order. The mixture was stirred for 10 min and used immediately to avoid the agglomeration. The GNP may also be stored at 4°C in an amber glass

Throughout the synthesis, the gold solution changed its color from light yellow (**Figure 2a**) to wine red (**Figure 2b**). This is a characteristic of the GNP formation [26].

For the seeding process, 100 ml of GNPs and 10 ml of functionalized silica were magnetically stirred in a 140 ml glass flask for 5 min as shown in **Figure 3a**. Then, it was left still for 2 h. **Figure 3b** presents how the seeded silica spheres precipitated and changed their color from opaque white to lavender, while the mother solution changed from wine red to transparent. The mixture was centrifuged at 6000 rpm for 2 min and washed in deionized water three times. Finally, it was sonicated in 20 ml of deionized water final volume. The same procedure was followed, but the solution was left still for only 30 min to observe the development of the seeding process through time.

For the shell growth process, a gold hydroxide solution was prepared by mixing 100 ml of 2 mM K2CO3 solution and 1.5 ml of 1% HAuCl4 in a 140 ml glass flask for

*Synthesis of GNPs at (a) the beginning of the reaction and (b) after 10 min of reaction.*

Finally, they were sonicated in 20 ml of deionized water final volume.

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**Figure 2.**

The shell was developed from the gold seeds deposited over the functionalized silica particles with the help of the Au(OH)4¯ ions. About 100 ml of the gold hydroxide solution (**Figure 5a**) and 5 ml of seeded silica were magnetically stirred in a 140 ml glass flask for 5 min (**Figure 5b**). Next, 5 ml of formaldehyde was added to the solution (**Figure 5c**) and stirred for 10 min (**Figure 5d**). The solution was left still for 50 min. Finally, it was centrifuged at 6000 rpm for 2 min, washed, and dispersed in 10 ml of deionized water final volume.

#### **Figure 4.**

*Images illustrating the change of color of the gold hydroxide solution at (a) the beginning of the synthesis (light yellow) and (b) 30 min of reaction (transparent).*

#### **Figure 5.**

*Images of the shell growing process. (a) Gold hydroxide solution, (b) gold hydroxide + seeded silica, (c) gold hydroxide + seeded silica + formaldehyde, and (d) solution after 10 min of reaction.*

#### **Figure 6.**

*Images of the installation of the (a) 820 nm wavelength laser, (b) non-contact digital IR thermometer, (c) connection to the multi-channel laser source, and (d) selection of the channel with the desired wavelength.*

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**Figure 7.**

*A Simple Way to Produce Gold Nanoshells for Cancer Therapy*

thermometer was also secured and directed to the GNS (**Figure 6b**). Next, the laser was connected to the Multi-channel laser source (**Figure 6c**). Finally, the channel with the desired wavelength was selected (**Figure 6d**), and the irradiation was started.

TEM images obtained from the silica samples taken at 30, 60, 90, and 120 min after adding the TEOS are presented in **Figure 7**. When comparing the images, no

To corroborate that the silica particles do not change substantially when the reaction time is over 30 min, the images were studied with the software Image J®, and the diameter distribution of the particles was analyzed. Over 1000 particles from the different samples were measured to obtain the histograms presented in **Figure 8** where samples A, B, C, and D correspond to 30, 60, 90, and 120 min of reaction time, respectively. They illustrate that the diameter distribution of the silica spheres

throughout the synthesis oscillates around the 190 ± 5 nm on all the samples. To have a better understanding of the information, **Table 1** contains useful

*TEM images of silica particles at (a) 30, (b) 60, (c) 90, and (d) 120 min after adding TEOS.*

significant variation in the size of the silica particles is noticeable.

*DOI: http://dx.doi.org/10.5772/intechopen.82495*

**4.1 Characterization of the silica templates**

statistic information from the samples.

**4. Results and discussion**

#### **3.9 Thermography**

To obtain the IR images, first, the 820 nm wavelength laser was fastened to the support for it to aim directly to the sample (**Figure 6a**). Then the Digital IR thermometer was also secured and directed to the GNS (**Figure 6b**). Next, the laser was connected to the Multi-channel laser source (**Figure 6c**). Finally, the channel with the desired wavelength was selected (**Figure 6d**), and the irradiation was started.
